The present invention relates to a zirconium crucible for melting an analytical sample, a method of preparing such analytical sample, and a method of analysis that enables the analysis of high purity samples by inhibiting the inclusion of impurities from the crucible and regardless of difference in the analysts and their skill.
In recent years, demands for measuring high purity materials quickly and accurately are on the rise. With the increase of such demands, there is a problem in that the measurement result will differ depending on skill of the analysts, and reanalysis must be performed from time to time in order to confirm the reliability of the initial analysis.
A sample for analysis is generally prepared by melting the sample with a flux. The process of melting the sample with a flux is usually based on a melting method such as carbonate (alkali) fusion, alkali hydroxide fusion, sodium peroxide fusion, or sodium hydrogensulfate fusion.
Among the above, sodium peroxide has strong oxidizing power, and is a favorable flux. Although an iron or nickel crucible is often used as the melting crucible in the foregoing case, it is necessary to take into consideration that the crucible will be severely affected.
Although the ratio of mixing this sodium peroxide fusion will differ depending on the nature of the sample, generally, 5 to 10 parts in weight of sodium peroxide is used in relation to the sample weight (Non-Patent Document 1). In addition, the heating temperature must also be changed according to the sample, and this is decided entirely by experience.
Conventionally, although the quantitative value was sought by subtracting the blank of the crucible, variation in the blank depends largely on the skill of the analyst. Further, since a conventional zirconium crucible has a purity level of 99 wt % (2N), impurities from the crucible would get mixed in, the lower limit of determination would become high as a result of the mixture of such impurities, and this was insufficient for the analysis of recent high purity samples.
Although there are not many Patent Documents that describe an analytical means to handle the foregoing high purity materials, to introduce some materials that may be of reference, for instance, there is technology that relates to the method of adjusting a sample for performing qualitative and quantitative analysis of such sample, whereby the sample is placed on a metal foil and subject to thermolysis together with such metal foil, and further made into a solution (Patent Document 1). Nevertheless, this is an extremely atypical type of method, and lacks versatility.
Further, a chemical analysis crucible composed from Pt alloy or Pd alloy in which 5 to 90 wt % of Pd is added to Pt that uses an alkali flux to perform chemical analysis of ores is disclosed (Patent Document 2). Nevertheless, this technology is subject to the use of expensive crucible materials, and there is a problem in that it is impractical since an alloy will be formed depending on the sample elements.
In addition, a method of analyzing the rhodium content in a film by heating and melting a rhodium-ruthenium alloy plating film in a nickel crucible with sodium peroxide or potassium peroxide is disclosed (Patent Document 3). Nevertheless, Patent Document 3 does not in any way disclose the purity of the crucible. Thus, it is strongly assumed that the crucible of Patent Document 3 has a conventional purity level (2N level). Thus, there is a problem in that the lower limit of determination is high due to the inclusion of impurities, and high precision analysis cannot be performed.    [Non-Patent Document 1] “Analysis” Introductory Course, Issued in Oct. 1979, “Reagent Used in Dissolution” Pages 648 to 655    [Patent Document 1] Japanese Patent Laid-Open Publication No. H10-38773    [Patent Document 2] Japanese Patent Laid-Open Publication No. H2-172540    [Patent Document 3] Japanese Patent Laid-Open Publication No. S58-48854